A scintillation crystal is a material which can convert X-ray particles or γ-ray particles into visible light photons, including Bismuth Germanium Oxide (BGO), Sodium Iodide (NaI)(Tl), Caesium Iodide (CsI)(Tl), LSO/LYSO, PbWO4(PWO) and so on. Scintillation crystals generally have characteristics such as strong absorptive capacity for a radiation, large optical output, and a linear relationship between the number of output photons and energy of the absorbed radiation.
A detector generally consists of the scintillation crystal and a photoelectric conversion device, and is applied to the field such as nuclear medicine field, environment monitoring field, customs security check field or geologic prospecting field. In the detector, the scintillation crystal absorbs energy of the radiation and generates a certain number of visible light photons associated with the absorbed energy. The photoelectric device is configured to receive the photons and convert the photons into an electrical signal, and the electrical signal is analyzed by a circuit to acquire energy, timing and other information of the radiation. The signal-to-noise ratio of the electrical signal directly correlates with the number of photons received by the photoelectrical device, and has a direct influence on performance of the detector. It is desired that the detector is so designed that all the photons generated in the scintillation crystal are able to be received and converted into the electrical signal, to improve the performance of the detector.
In the Positron Emission Tomography (PET), when more output light of the scintillation crystal gets into the photoelectric device, precision of acquiring information on energy of γ-photon can be enhanced, and therefore imaging quality is improved. Therefore, it is very important for improving performance of the PET system to seek for a method or a detecting structure in which the output light of the scintillation crystal gets into the photoelectric device as much as possible.
For an practical application, an array photoelectric conversion face having the large detection area is constructed by arranging multiple photoelectric conversion devices together. The current common photoelectric conversion device includes silicon photomultipliers, avalanche photodiodes, photomultipliers and so on. This kind of photoelectric conversion device has a photoelectric accepting window smaller than the overall surface thereof. A photoelectric detection dead zone exists in detection surface in a case that the array photoelectric conversion face is constructed by patching multiple photoelectric conversion devices together. Hence the photoelectric detection face is not continuous, and some regions can not accept the photons. For example, in FIG. 1, the area of active region 100 of the silicon photomultiplier is 3×3 mm2, and the area of a whole package surface 200 thereof generally reaches 4×4 mm2. In a case that such photoelectric conversion devices are used to constitute a photoelectric conversion array, the photoelectric detection face of the array is discontinuous, and package dead zones are formed between the discontinuous photoelectric detection area. Therefore, when a detector is constructed with this kind of photoelectric conversion array, in a case that a coupling mode in which a single crystal corresponds to multiple photoelectric devices is employed, a part of visible light photons formed in a crystal strip may reach the package dead zone and can not contribute to the effective electrical signal, which reduces the performance of the detector.
In view of this, in a practical application, crystal strips are often coupled to photoelectrical devices in a one-to-one relationship, and the crystal strips are arranged to construct an array. Information relating to the high-energy particle is acquired by detecting an output signal of the photoelectric device. Currently, there are mainly the following two ways for constructing a crystal-array for the application described above.
One way is to employ crystal strips each having the same size of the package of a photoelectric device to construct the array crystal. As shown in FIG. 2, the size of a single crystal strip 300 in the crystal-array is the same as an overall size of a single photoelectric device 400, an effective detection region 500 is then provided. Due to the existence of a detection dead zone of the photoelectric detector, a part of photons formed in the crystal can not be accepted by the photoelectric detector, and the performance of the detector is deteriorated. However, since the gap between crystal strips is small in the detector, the volume of the scintillation crystal for detecting a high-energy particle is large, and the detection efficiency is still relatively high.
Another way is to use a coupling mode in which a crystal strip 800 has the same size of an effective detection region 700 of a photoelectric device 600. As shown in FIG. 3, in this way, a light output face of the crystal strip is coupled to the effective detection region 700 of the photoelectric device perfectly. Therefore, the performance deterioration due to a detection dead zone of the photoelectric device is avoided. However, a gap between crystal strips is large, the volume of the scintillation crystal for detecting a high-energy particle is reduced, leading to the decline of detection efficiency.
Therefore, for the technical problem described above, it is desired to provide a crystal-array module having an improved structure to solve the defect described above.